ANSI/ISA S84.01-1996 and drafts IEC 61508/61511 are standards covering the design, operation, maintenance, and testing of safety instrumented systems (SIS). The standards stress the importance of minimizing potential faults in the SIS through good design and engineering practice. These faults include random hardware, systematic, and common cause faults. Common cause faults occur when a single f...

We describe CRESCO, a tool for Construction of Evidence REpositories for Managing Standards COmpliance. CRESCO draws on Model Driven Engineering (MDE) technologies to generate a database repository schema from the evidence requirements of a given standard, expressed as a UML class diagram. CRESCO in addition generates a webbased user interface for building and manipulating evidence repositories...

SIL's (Safety Integrity Levels) are used by IEC 61508:1998 [1] to characterise the required functional safety of computer control systems. For example, SIL 4, the highest rating is for fly by wire aircraft and weapons systems and track circuited train signalling systems while SIL 2 is typical of certain Programmable Logic Controllers (PLC). Fire control panels have not been SIL rated to date ev...

IEC 61508-7 [1] includes as Annex D a proposal for the evaluation of software reliability based on a simple statistical model. However, this annex is discussed quite controversially and is currently under revision. EN 50129 [2] also contains recommendations on how to demonstrate high confidence by use, but without any further explanation. For example, for SIL 3 and 4, “1 million hours operation...

The international standard for functional safety of systems involving programmable-electronic components, IEC 61508, has been valid since the late 1990's, and Version 2 has just become valid [IEC10]. The scope of the standard is, generally, everything except avionics and medical equipment. It is based on the approach, novel at that time, of quantifying and reducing risk until it is acceptable, ...

ANSI/ISA-S84.01-1996 and IEC 61508 require the establishment of a safety integrity level for any safety instrumented system or safety related system used to mitigate risk. Each stage of design, operation, maintenance, and testing is judged against this safety integrity level. Quantitative techniques can be used to verify whether the safety integrity level is met. ISA-dTR84.0.02 is a technical r...

Programmable electronic systems (PESs) that are currently employed in safety-critical applications follow either a strictly periodical or a task-based operating policy. This paper discusses these policies with regard to safety aspects and introduces a novel real-time execution concept that combines their advantages. The main characteristics of this new concept are quantisation of time into disc...

The aim of the international standard IEC 61508 is to provide a route whereby safety-related systems can be implemented using electrical or electronic or programmable electronic technology in such a way that an acceptable level of functional safety is achieved. The strategy of the standard is first to derive the safety requirements of the safety-related system from a hazard & risk analysis and ...

A safety instrumented system (SIS) is a complex unit composed of set hardware and software controls which are expressly used in critical process systems. SIS should be specifically designed to obtain the failsafe state monitored plant or maintain procedure when unacceptable dangerous conditions occur. This paper focuses on condition monitoring different diagnostic solutions systems, such as lim...